/*	Interactive Gravitational Simulator
	Project: IGS Core
	File: Leapfrog.cpp
	Author: Mike Bantegui <mbante2@gmail.com>, Hofstra University 
	Copyright (C) 2012 - 2013 Mike Bantegui

	This file is part of the IGS software package for simulating
	the N-Body problem in real-time. This was developed as part
	of a departmental honors thesis project at Hofstra University
	in the Spring 2012 semester.

	IGS is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	IGS is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, write to the Free Software
	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

#include "Leapfrog.h"
#include "Body.h"

namespace IGS
{

// Destructs the Leapfrog integrator
Leapfrog::~Leapfrog()
{
}

// r(t + dt) = r(t) + dt * v(t) + 1/2 * dt^2 * a(t)
// vp(t + dt) = v(t) + dt * a(t)
void Leapfrog::Predict(const WorldPoint &start, WorldPoint &end) const
{
	double dt = end.Time - start.Time;
	end.Position = start.Position + dt * start.Velocity + (dt * dt / 2) * start.Acceleration;
	end.Velocity = start.Velocity + dt * start.Acceleration;
}

// v(t + dt) = v(t) + 1/2 * dt * (a(t) + a(t + dt))
void Leapfrog::Correct(const WorldPoint &start, WorldPoint &end) const
{
	double dt = end.Time - start.Time;
	end.Velocity = start.Velocity + (dt / 2) * (start.Acceleration + end.Acceleration);
}

// Returns the name of the Leapfrog integrator
std::string Leapfrog::Name() const
{
	return "Leapfrog";
}

}